torie, it is not the water you drink, it is the water in which you wash: shower, pool, river and so on. all those can be contaminated. as a result a small mosquito bite or an irritated area can get infected.
if you do not see a dermatologo you risk repeated infections. some of the areas (face and the head) can be very dangerous too if affected. dr1ers can advice you an english speaking dermatologo (i know a decent one in POP, others can point you good doctors in different cities).
i suggest you try some antibiotic cream (most likely that's what you'd get anyways). maybe fucidin? it costs about 500-700 pesos. there are some cheaper creams with antibiotics too, like derma3 but they also contain anti fungal meds. clean the area, apply cream twice a day. use talc to keep general area dry. use only cotton for now and at home take off the shirt altogether.